Are hydraulic fittings pipe thread pitch or other?

My dealer made up some hydraulic hoses for me. He put ends on the hoses that are threaded, with an outside diameter of 3/4". The inside diamter is about 1/2" (I'm not sure how to correctly refer to this, should I call these fittings 3/4" or 1/2"?)

Anyway, my main question is this: I was told that these were pipe thread fittings. I think that is correct, as I remember hearing that pipe threads are tapered, with the end of the fitting being slightly tapered in. When I look closely at these fittings they do indeed appear to be tapered.

When I turn these male pipe thread fittings into a female pipe thread fitting, they seem to fit very well. The fitting turns several times before "bottoming out".

However, When I turn this same male pipe thread fitting into either flat front hydraulic connector, or a ball/poppel style hydraulic connector, it turns only about 1 1/2 turns before stopping.

Are hydraulic fittings usually pipe thread or some other thread pitch/taper? Something just doesn't seem right here, and I don't want to wrench on it before I'm certain.

Re: Are hydraulic fittings pipe thread pitch or other?

some are pipe thread (tapered) and some are a straight thread like would be an a bolt. The straight thread require an "O" ring, washer and a jam nut to seal it. Straight threads allow a fitting such as an elbow to be poistioned exactly where you want it. You can get the mating half either way also.

Re: Are hydraulic fittings pipe thread pitch or other?

Just to clear up any confusion (and maybe cause some more [img]/forums/images/graemlins/blush.gif[/img]), your threads are NPTF, most likely 1/2". Here is a description of the different pipe threads.

NPTF
This is a dryseal thread; the National pipe tapered thread for fuels. This is used for both male and female ends. Several trade associations no longer recommend this thread connection for use with hydraulics but it is still widely used and fittings are easy to obtain and connection combinations cover the entire spectrum of types.

The NPTF male will mate with the NPTF, NPSF, or NPSM female.

The NPTF male has tapered threads and a 30° inverted seat. The NPTF female has tapered threads and no seat. The seal takes place by deformation of the threads. The NPSM female has straight threads and a 30° inverted seat. The seal takes place on the 30° seat.

The NPTF connector is similar to, but not interchangeable with, the BSPT connector. The thread pitch is different in most sizes. Also, the thread angle is 60° instead of the 55° angle found on BSPT threads.

NPSF
The National pipe straight thread for fuels. This is sometimes used for female ends and properly mates with the NPTF male end. However, the SAE recommends the NPTF thread in preference to the NPSF for female ends.

NPSM
National pipe straight thread for mechanical joint. This is used on the female swivel nut of iron pipe swivel adapters. The leak-resistant joint is not made by the sealing fit of threads, but by a tapered seat in the coupling end.

Even though NPTF fittings are dryseal, almost everyone uses some type of thread sealant when used in hydraulic applications.

Re: Are hydraulic fittings pipe thread pitch or other?

MadReferee,

Thanks for the info. I have three types of hydraulic fittings that I need to mate to my pipe thread hydraulic cable ends.

The first type is a male poppel/ball connector. It has a long part number stamped on it which includes the characters "1/2" and "NPTF", so that one appears to be a match for my lines. Two of these will be used to connect to the remote hydraulic connectors of my tractor.

The other two fittings are a male and a female flat front connector. Those are stamped "UM Parker FEM-502-8FP" on the male, and "PL Parker FE-501-8FP-NL" on the female.

I'm going to try to find a web site for Parker, and see if it lists what thread pitch these connectors are supposed to be.

Re: Are hydraulic fittings pipe thread pitch or other?

Pieces of teflon tape can tear off and float through your hydraulic system. Also, tape is primarily for lubricating a joint as it is tightened, and does not provide much in the way of sealing. Paste does a much better job of sealing a joint.

Re: Are hydraulic fittings pipe thread pitch or other?

Just as DocHeb said. Teflon paste will lube as it seals and any that manages to get into the fluid will be dispersed/disolved and not clog up any filter or pump like teflon tape will. It is typically good up to pressures of 3000 psi and will tolerate extreme temperature changes without hardening or turning to liquid.

A small 4oz container of paste will last a lifetime and only cost a couple of bucks at any hardware store.